linux-kernel - Re: [PATCH -next v4 0/2] support allocating crashkernel above 4G explicitly on riscv

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Message-ID: <db4ba964-1c09-1d8a-bfc4-8fe50debfc6c@huawei.com>
Date:   Tue, 25 Apr 2023 21:20:53 +0800
From:   "chenjiahao (C)" <chenjiahao16@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <kexec@...ts.infradead.org>, <linux-doc@...r.kernel.org>
CC:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <conor.dooley@...rochip.com>, <guoren@...nel.org>,
        <heiko@...ech.de>, <bjorn@...osinc.com>, <alex@...ti.fr>,
        <akpm@...ux-foundation.org>, <atishp@...osinc.com>,
        <bhe@...hat.com>, <thunder.leizhen@...wei.com>, <horms@...nel.org>
Subject: Re: [PATCH -next v4 0/2] support allocating crashkernel above 4G
 explicitly on riscv


On 2023/4/10 21:05, Chen Jiahao wrote:
> On riscv, the current crash kernel allocation logic is trying to
> allocate within 32bit addressible memory region by default, if
> failed, try to allocate without 4G restriction.
>
> In need of saving DMA zone memory while allocating a relatively large
> crash kernel region, allocating the reserved memory top down in
> high memory, without overlapping the DMA zone, is a mature solution.
> Hence this patchset introduces the parameter option crashkernel=X,[high,low].
>
> One can reserve the crash kernel from high memory above DMA zone range
> by explicitly passing "crashkernel=X,high"; or reserve a memory range
> below 4G with "crashkernel=X,low". Besides, there are few rules need
> to take notice:
> 1. "crashkernel=X,[high,low]" will be ignored if "crashkernel=size"
>     is specified.
> 2. "crashkernel=X,low" is valid only when "crashkernel=X,high" is passed
>     and there is enough memory to be allocated under 4G.
> 3. When allocating crashkernel above 4G and no "crashkernel=X,low" is
>     specified, a 128M low memory will be allocated automatically for
>     swiotlb bounce buffer.
> See Documentation/admin-guide/kernel-parameters.txt for more information.
>
> To verify loading the crashkernel, adapted kexec-tools is attached below:
> https://github.com/chenjh005/kexec-tools/tree/build-test-riscv-v2
>
> Following test cases have been performed as expected:
> 1) crashkernel=256M                          //low=256M
> 2) crashkernel=1G                            //low=1G
> 3) crashkernel=4G                            //high=4G, low=128M(default)
> 4) crashkernel=4G crashkernel=256M,high      //high=4G, low=128M(default), high is ignored
> 5) crashkernel=4G crashkernel=256M,low       //high=4G, low=128M(default), low is ignored
> 6) crashkernel=4G,high                       //high=4G, low=128M(default)
> 7) crashkernel=256M,low                      //low=0M, invalid
> 8) crashkernel=4G,high crashkernel=256M,low  //high=4G, low=256M
> 9) crashkernel=4G,high crashkernel=4G,low    //high=0M, low=0M, invalid
> 10) crashkernel=512M@...0000000              //low=512M
> 11) crashkernel=1G@...0000000                //high=0M, low=0M, no enough low memory, failed
>
> Changes since [v4]:
> 1. Update some imprecise code comments for cmdline parsing.
>
> Changes since [v3]:
> 1. Update to print warning and return explicitly on failure when
>     crashkernel=size@...set is specified. Not changing the result
>     in this case but making the logic more straightforward.
> 2. Some minor cleanup.
>
> Changes since [v2]:
> 1. Update the allocation logic to ensure the high crashkernel
>     region is reserved strictly above dma32_phys_limit.
> 2. Clean up some minor format problems.
>
> Chen Jiahao (2):
>    riscv: kdump: Implement crashkernel=X,[high,low]
>    docs: kdump: Update the crashkernel description for riscv
>
>   .../admin-guide/kernel-parameters.txt         | 15 ++--
>   arch/riscv/kernel/setup.c                     |  5 ++
>   arch/riscv/mm/init.c                          | 71 +++++++++++++++++--
>   3 files changed, 79 insertions(+), 12 deletions(-)

Hi folks,

The current version has fix all problems up-to-date, please let me know
if there is any other bug, or somewhere not quiet correct. Thanks for
looking into this.

Best Regards,
Jiahao